Modern brake-assistance and driving dynamics systems almost exclusively use oscillating positive displacement pumps as high pressure generating unit. Leakage passes over a circumference of a piston and along a guide length in a stationary cylinder.
Rotating positive displacement pumps have axial and radial leakage gaps between individual chambers of the displacement gear components. Internal gear pumps have leakage gaps for example axially on the end sides of the gear wheels, i.e. of the pinion and of the ring gear. This results in a conflict of objectives between minimal leakage and minimal friction of the rotating positive displacement pump.
DE 10 2013 201 384 A1 discloses an internal gear pump for a hydraulic vehicle brake system, having a pump shaft on which a pinion is arranged for conjoint rotation, having a ring gear which meshes with the pinion, and having a rotationally fixed axial disk which is arranged on and bears in a sealing manner against an end side of the pinion and of the ring gear.